What do tachycardiomyopathy belong to?

We read with interest the new classification of cardiomyopathies proposed by the European Society of Cardiology (ESC) working group on myocardial and pericardial disease,1 which certainly represents a praiseworthy step towards a more clinically oriented classification system that overcomes some of the limitations of the recent American Heart Association classification. However, a controversial point concerning both classifications is represented by the inclusion of tachycardiomyopathy (TCMP) in the group of ‘primary cardiomyopathies’. The ESC classification define cardiomyopathy as a ‘… myocardial disorder in which the heart muscle is structurally and functionally abnormal …’, excluding pathological myocardial processes and dysfunctions that are a direct consequence of other cardiovascular abnormalities such as valvular heart disease, systemic hypertension, and coronary artery disease. According to this definition, TCMP should not be included in the group of primary cardiomyopathies as clinical evidence, and experimental studies clearly demonstrate that myocardial dysfunction is associated with the occurrence and persistence of abnormally increased heart rate in the context of supraventricular and ventricular tachyarrhythmias.2,3 Experimental models of TCMP have shown that chronic rapid pacing produces a severe reversible cardiomyopathy sustained by transient functional and structural changes of myocytes including cellular elongation and myofibril misalignment.4,5 Similarly, in patients, tachyarrhythmias can cause a severe cardiac dysfunction which, however, recovers in the weeks following the termination or rate control of tachyarrhythmias. Accordingly, the diagnosis of TCMP requires the demonstration of left ventricular function improvement after treatment of arrhythmias, thus excluding other mechanisms contributing to cardiac dysfunction. Indeed, the absence of complete recovery of left ventricular function after termination of tachyarrhythmias suggests the presence of a previously unrecognized underlying myocardial disease made clinically evident by the occurrence of tachyarrhythmias. That may be the case in patients with subclinical forms of idiopathic or inflammatory dilated cardiomyopathy, in which a persistent increase in heart rate may produce clinical symptoms in previously asymptomatic subjects. Of note, concealed cardiomyopathies may represent the substrate of tachyarrhythmias eventually leading to a progressive deterioration of clinical picture and precipitating non-reversible morpho-functional ventricular abnormalities. Although the complex link between electrical properties, mechanical function, and structural integrity of myocardial cells needs further clarification, TCMP, at the present time, should be excluded from primary cardiomyopathies in the current ESC classification, similarly to what is the case for ion-channel disorders.